I am over level 39, so I can no longer spawn level 42 master vampires, but I was wonder if I could retain some lower-level master vampires and level them to 42 so I could use the bounty glitch to move them to the next tier.

Honestly, I'm not 100% sure if your dead thralls even level with you, but if they do, is it possible to level a lower-level vampire master to 42? If so, how would I go about doing it?